linux-kernel - Re: [PATCH v3] kdb: Replace deprecated strcpy() with strscpy() and memcpy()

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Message-Id: <710CDE93-89CC-4B60-A582-5F9B2916ED72@linux.dev>
Date: Fri, 15 Aug 2025 13:28:01 +0200
From: Thorsten Blum <thorsten.blum@...ux.dev>
To: Daniel Thompson <daniel@...cstar.com>
Cc: Jason Wessel <jason.wessel@...driver.com>,
 Daniel Thompson <danielt@...nel.org>,
 Douglas Anderson <dianders@...omium.org>,
 Nir Lichtman <nir@...htman.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Yuran Pereira <yuran.pereira@...mail.com>,
 linux-hardening@...r.kernel.org,
 kgdb-bugreport@...ts.sourceforge.net,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] kdb: Replace deprecated strcpy() with strscpy() and
 memcpy()

Hi Daniel,

> On 15. Aug 2025, at 10:57, Daniel Thompson wrote:
> Sorry but a strscpy() where the length of the destination buffer has
> been calculated from the source string is way too much of a red flag
> for me.
> 
> Put another way if there are "no functional changes intended" then there
> cannot possibly be any security benefit from replacing the "unsafe"
> strcpy() with the "safe" strscpy(). Likewise abusing the destination
> length argument to truncate a string makes the code shorter but *not*
> clearer because it's too easy to misread.

Deliberately truncating the source using strscpy() is a valid use case.
strscpy() allows the size argument to be smaller than the destination
buffer, so this is an intended use of the size argument, not an abuse.

From the strscpy() function comment in linux/string.h:

* The size argument @... is only required when @dst is not an array, or
* when the copy needs to be smaller than sizeof(@dst).

Thanks,
Thorsten